An inkjet recording method has been rapidly spread and is still developing because it requires inexpensive materials, it enables one to conduct rapid recording, it generates less noise upon recording, and because it permits color recording with ease. The inkjet recording method includes a method of continuous type wherein liquid droplets are continuously ejected and a method of on-demand type wherein liquid droplets are ejected in response to image information signals. Also, the ejection method includes a method of ejecting liquid droplets by applying pressure through piezo elements, a method of ejecting liquid droplets by generating a bubble in an ink through heat, a method of using ultrasonic waves and a method of attracting and ejecting liquid droplets by electrostatic power. As an ink for these inkjet recording methods, there are used aqueous inks, oily inks or solid (melting type) inks.
Colorants to be used in these inks for the inkjet recording method are required to have a high solubility in a solvent such as water, realize high-density recording, provide a good hue, have excellent fastness against light, heat, active gases in the environment (e.g., oxidative gases such as NOx and ozone, and SOx), water and chemicals, show an enough good fixability for an image-receiving material not to be blurred, have an excellent keeping quality as an ink, have no toxicity, have a high purity and be available at a low price.
In particular, it has eagerly been required for dyes to have excellent fastness against light, humidity, heat and, particularly in the case of printing on an image-receiving material having an ink receptive layer containing porous, white inorganic pigment particles, oxidative gases in the environment such as ozone, and have an excellent water resistance.
On the other hand, it has been known that, in the case of forming a recorded image having a high optical density, dye crystals precipitate on the surface of the recording material as the recording material is dried and, as a result, the recorded image reflects light to give metallic luster, which is called the problem of bronze phenomenon. This phenomenon tends to take place when solubility of the dye in water is reduced or when a hydrogen bond-forming group is introduced into the structure of the dye for the purpose of improving resistance to water, light or gas. Since the bronze phenomenon causes reflection or scattering of light, the recorded image suffers not only reduction of optical density but also serious change in hue from desired hue and loss of transparency. Thus, depression of the bronze phenomenon is one of important factors required for the ink for use in inkjet recording.
As methods for depressing the bronze phenomenon, there have so far been known a method of adding a specific, nitrogen-containing compound (see, for example, JP-A-6-25575, JP-A-6-228476, JP-A-6-248212, JP-A-7-228810, JP-A-7-268261, JP-A-9-12946 and JP-A-9-12949), a method of adding a specific, hetero ring compound (see, for example, JP-A-8-259865, JP-A-2004-149612 and JP-A-2004-149613), a method of adding a specific titanium-containing compound (see, for example, JP-A-8-337745), and a method of adding an alkali metal ion (see, for example, JP-A-7-26178). However, although the bronze phenomenon can be depressed by adding these additives, the amounts thereof tend to become large due to their insufficient effects, or there arises a problem with respect to storage stability. Thus, the methods can deteriorate various performances of the ink and the quality of recorded images. For example, in the case of adding an alkanolamine to the ink, pH of the ink becomes as high as 11 or more even when it is added in only a small amount. It is described in JP-A-8-259865 that an ink having such a high pH adversely affects the nozzle and, in addition, lacks safety in the case when it is accidentally touched by a human body, and reduces quality of printed letters and resistance to water of recorded images.
Although various effects can be obtained by using the additives, it has been difficult to use the additives of the related art with maintaining various performances. In particular, in the case where it is necessary to take solubility and association of a dye into consideration, it can be seen that selection of kind and amount of the additive are difficult. Also, in the case of using an ionic additive, influences of the counter ion thereof must be taken into consideration as well. Therefore, it has been desired to introduce a method of essentially depressing the bronze phenomenon by designing a molecule of the additive based on a novel idea.
Further, as a method for depressing bronze phenomenon caused by a cyan dye or the like, there has been known a method of using a compound having a carboxyl group (EP-A-1357158). However, the compounds serve to depress bronze phenomenon with respect to dyes of a comparatively longer wavelength such as cyan dyes and, as to bronze phenomenon caused by the yellow dye, nothing is described therein.